Name: Larissa Santos Coutinho Jorge
Type: MSc dissertation
Publication date: 19/12/2022

Namesort descending Role
Elisa Valentim Goulart Advisor *

Examining board:

Namesort descending Role
Bruno Furieri Internal Examiner *
Elisa Valentim Goulart Advisor *
Lya Lugon Cornejo Vom Marttens External Examiner *
Neyval Costa Reis Jr. Co advisor *

Summary: The present study evaluates the flow and dispersion of a scalar within an array of obstacles. Numerical simulations are performed using a transient street network model, whose
basic idea is to divide an urban area into connected boxes, which can be streets or intersections. The purpose of the model is to provide the average concentration values within each
location. In real situations, wind velocity can present itself in a highly variable way, in time
and space. In this way, modeling this information is not simple. In terms of approaches
based on CFD, results obtained from DNS (Direct Numerical Simulation) are more representative of reality, since in this method all scales of a turbulent flow are resolved. Thus,
in the present study, the flow and dispersion of a passive scalar through a network of streets composed of rectangular buildings were evaluated. Initially, an analysis of the general
characteristics of the flow and dispersion within the canopy was carried out, through the evaluation of the temporal evolution of the velocities, responsible for the advective transport. It
was verified that the velocities present a highly three-dimensional and fluctuating character
among the streets of the array, with the greatest fluctuations occurring in regions of street
intersections. About the dispersive process, the results showed the influence of topological
dispersion on the distribution of the scalar plume within the canopy, in which the intersection
regions act by amplifying the transport to subsequent streets. The applicability of the street
network model was verified from comparisons with DNS data, demonstrating its ability to
predict concentrations and the general behavior of the plume, WHERE the main aspects associated with dispersion were evidenced. Thus, to identify the influence of velocities on scalar
dispersion, reference data from DNS simulations were adopted to obtain the results of the
street network model. The velocities are characterized by four different heights, 0.03125H,
0.25H, 0.5H, and 0.75H. In general, the concentration levels were more significant in places around the emission site. In addition, it was observed that as the velocity input data
changed, there were changes in the dispersive process, especially in the temporal and spatial
variability of the scalar between the canopy streets. Finally, changes in the fluctuation levels
of concentration within the canopy were also identified. It was evidenced that the concentration fluctuations were more intense throughout the canopy, for the most stochastic velocity
field, with the most significant occurring for velocities in regions close to the ground.

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